1906.] PLACENTA IN UNGULATES. 95 



(5) " The layer in question is clearly not an attenuation of an 

 ordinary epithelium," and is not secretory, as, e. g., is the 

 epithelium lining the crypts in the Cow, which Assheton 

 admits to be of uterine origin. 



As explained in the body of the paper, my own observations do 

 not permit me to speak at first-hand of the oiigin of the cells lining 

 the crypts in the principal maternal cotyledons. I am, however, 

 certain that in the accessory cotyledons of the Cow the crypts are 

 lined by an epithelium which is a modified uterine epithelium, and 

 that in the piincipal cotyledons of both Cow and Sheep the extra- 

 cotyledonary columnar uterine epithelium is perfectly continuous 

 with the modified epithelium of the crypts. The latter in the 

 Cow is simply cubical ; in the Sheep it is more seriously altered, 

 flattened, and often interrupted. There are places, however, in 

 which the cells retain, as I should put it, their columnar form ; 

 and from these cell-nests diverticula are produced which line new 

 crypts. From these facts I have inferred that, in the principal 

 cotyledons, the lining is also of uterine origin. 



Still there is no necessary contradiction between this view 

 and that put forward by Assheton ; for it is perfectly conceivable 

 that the cells in question may originate in different ways in the 

 principal and accessory cotyledons, and that the continuity observed 

 in the former between exti-a- and intra-cotyledonary epithelia is 

 secondary. I do not think, however, that Assheton has proved 

 his, admittedly difficult, case ; for 



(1) Similarity in staining is not a very safe criterion ; other 



nuclei and cell-bodies — e. g., those of subepithelial cells — 

 often stain intensely ; also the nuclei of the binucleate 

 cells are often larger, more spherical, and paler than are 

 those of the cells lining the crypts, and in his fig. 40 

 Assheton figures nuclei of " plasmodiblast " cells which are 

 quite pale. 



(2) Vacuoles — of fat and glycogen — certainly occur in the 



uterine epithelial cells, both inside and outside the cotyle- 

 donary caruncles. 



(3) The nuclei of the layer lining the crypts do not always 



occur in pairs, but very frequently in heaps, in the cell- 

 nests I have alluded to, as Assheton's own figures show. 



(4) The lining epithelium of the crypts undoubtedly contains 



fat-globules, and fatty cellular debris is found in the ciypt 

 lumen ; these cells are therefore as certainly secretory here 

 as they are in the Cow. 



(5) The asserted degeneration of the uterine epithelium is very 



probably largely illusory. Where I had at first supposed 

 that the uterine epithelium had disappeared I have often 

 found subsequently that, by more careful preservation, it 

 could be demonstrated without difficulty. 



Although there is no inherent improbability in the account 

 given by Assheton, and indeed some such intermediate form 



